By Louis Charbonneau

UNITED NATIONS (Reuters) - If the International Criminal Court decides to indict Sudan's president for crimes in Darfur it could ruin a peace process that ended two decades of civil war, a senior U.N. official said on Wednesday.

Khartoum has already said that peace in its war-racked Darfur region would be impossible if the U.N. Security Council does not stop the ICC from indicting Sudanese President Omar Hassan al-Bashir for genocide and other war crimes in Darfur.

Sudanese officials have suggested that U.N.-African Union peacekeepers in Darfur, known as UNAMID, could be expelled if the judges indict Bashir. A separate U.N. force policing compliance with a peace deal that ended Sudan's north-south civil war had hoped they would be spared such retaliation.

But U.N. Assistant Secretary-General for Peacekeeping Edmond Mulet said both UNAMID and the other peacekeeping force in semi-autonomous south Sudan, known as UNMIS, could become targets of revenge if a warrant is issued for Bashir's arrest.

Mulet told the U.N. Security Council that the ICC chief prosecutor's request for Bashir's indictment "could have serious security and other implications for UNMIS and UNAMID."

"(It) could potentially derail the CPA process," he said, referring to the 2005 Comprehensive Peace Agreement that ended 20 years of civil war that resulted in the deaths of some 2 million people across Africa's largest country.

"We are concerned about the suggestions of an uncontrolled reaction to an indictment by the population against UNMIS," Mulet said.

"We are also concerned by statements of government officials of an intention to expel U.N. staff members ... thought to have cooperated with the ICC, even though they are performing their authorized functions as directed by the Security Council," he said.

DISPUTE OVER OIL REGION

The CPA appeared to be in jeopardy earlier this year when northern and southern troops clashed in the oil-rich region of Abyei. That conflict was eventually defused and UNMIS plans to shift more troops there to prevent a renewal of fighting.

Sudanese nationwide elections are scheduled for next year and a referendum on whether the south should secede from Sudan is expected to take place in 2011. But the status of Abyei and who should have control over the oil wealth remains unresolved.

U.N. officials have told Reuters that if UNMIS is expelled from Abyei, northern and southern Sudanese troops might resume fighting over the region in a bid to seize control of the oil.

In July, ICC Chief Prosecutor Luis Moreno-Ocampo charged Bashir with orchestrating a campaign of genocide in the Darfur region beginning in 2003 that has killed 35,000 people outright and at least another 100,000 through starvation and disease.

The charges include war crimes, crimes against humanity and genocide. U.N. officials say the Darfur conflict has left as many as 300,000 dead and 2.5 million homeless since mostly non-Arab rebels took up arms against the government in 2003.

Bashir says the charges against him were fabricated. He has had support from the African Union, Arab League and other alliances, which have urged the Security Council to block the ICC moves to protect the fragile Darfur peace process.

The ICC judges are not expected to make a decision on whether to indict Bashir before January.